1. Field of the Invention.
The present invention relates to an ultrafiltration regulation system for hemodialysis purposes, and more particularly, concerns an apparatus and method for regulating ultrafiltration during hemodialysis utilizing volumetric measurement by weight.
2. Description of the Prior Art.
Ultrafiltration is the procedure during hemodialysis wherein excess water is removed from the blood. It is well-known, for example, to achieve satisfactory ultrafiltration by maintaining the dialysate pressure within the dialyser lower than that of the blood pressure. During this procedure, while excess water in the blood is removable, the rate of ultrafiltration is a critical factor, since rapid removal of water from the blood may traumatically affect the patient. Various solutions to the control of the rate of ultrafiltration have been proposed, one of which is found in U.S. Pat. No. 4,021,341.
Other techniques for ultrafiltration regulation include continuously monitoring the weight of the patient during the treatment by means of an in-bed scale. Effective regulation of ultrafiltration, however, has been difficult to achieve using this aforementioned technique.
A different scheme for regulating ultrafiltration by a weighing technique is described in U.S. Pat. No. 4,132,644. This patented approach utilizes a closed liquid container, having a flexible liquid-tight bag within, and a suitable scale for indicating any change in the weight of the content of the container. In use, weight of the inflow of liquid is registered by the scale. After the dialyzing liquid flows through the dialyzer, spent liquid returns to the container. There is a volume of air in the space above the liquid-filled bag, but within the container, which is regulated by a suction pump. This enables a regulated removal of ultrafiltrate from the blood during the dialysis treatment. Since the container is being weighed, the weight of the liquid in the container will increase when ultrafiltrate is added thereto. Thus, the amount of ultrafiltrate can be monitored due to the increase of the total weight in the container. While this patented technique relies upon weight differentials to assess ultrafiltration characteristics, its operation is limited. Specifically, the closed fluid circuit requires a storage container for holding a limited quantity of liquid, which consists of both fresh dialysate and spent dialysate. No provision is made for continuous draining of the spent dialysate, since the container must be opened after the hemodialysis treatment has been completed so that the flexible liquid bag may be removed and then discarded.
Accordingly, improvements in the regulation of ultrafiltration, particularly utilizing volumetric measurement by weight, are still being sought. It is to such an improvement which the present invention is directed.